1. Field of the Invention
The present invention relates to an optical fiber array with lenses used in a field of optical communication.
2. Description of the Related Art
In recent years, technological innovation has been significant in information communication. To accommodate an increased communication speed and an increased amount of information communicated resulting from the spread of an Internet, communication has been shifting from the reliance on electric signals to the use of optical signals. More and more traditional cables, which were used as essential elements of many networks, have been replaced with optical ones because information from various relay points is gathered at the cables. Accordingly, the processing speed has been substantially improved. However, the communication between optical cables and user terminals is expected to be reviewed because there have been more and more exacting demands for the establishment of more inexpensive and comfortable information communication environments.
As the establishment of optical communication networks makes gradual progress, information is transmitted at higher speed. Correspondingly, more and more new applications are created. Furthermore, the amount of information communicated over the optical communication networks increases. To increase the amount of information that can be processed with optical fibers, high-frequency signals are used in order to increase the amount of signals available per unit time. Further, for the same purpose, a technology called a “wavelength division multiplex method” is used in which signals of a large number of wavelengths with different pieces of information are simultaneously transmitted through a single optical fiber. However, a large number of optical fibers must be used for communication involving an enormous amount of information that cannot be processed by the wavelength division multiplex method. Further, to form an elaborate and reliable communication network, it is necessary to establish connections to multiple paths in multiple directions. Thus, the use of a plurality of optical fibers is also essential in connection with maintenance applications.
To form an optical circuit using a plurality of optical fibers, an optical fiber array with the optical fibers arranged parallel with each other is often used in order to facilitate assembly operations. The use of an optical fiber array allows a plurality of optical fibers to be handled easily at a time, thus allowing connection operations to be performed more efficiently.
When an optical signal propagated through an optical fiber is emitted from an end of the optical fiber into a medium such as air or a liquid which has a refraction index different from that of the optical fiber, a light beam is spread. The spread of the light beam increases consistently with distance over which the signal propagates through the medium. Consequently, a propagation loss occurs when the optical signal is connected to a light beam path such as another optical fiber. A collimator lens is used to prevent the spread of the light beam. Optimizing the refraction index of the lens allows the light beam emitted from the optical fiber end to advance without being spread.
With an optical fiber array with lenses, a pitch interval must be matched between the arrangement of optical fibers and the arrangement of lenses. That is, the distance between the optical fibers arranged in an array must be equal to the pitch interval of the lenses. Further, to prevent the size of the circuit from being increased even with a plurality of optical fibers connected to each optical device part, the pitch of an optical path must be matched between the optical fiber array, in which the plurality of optical fibers are connected together, and the optical device part.
In an optical fiber array used to connect a plurality of optical fibers together, the connection pitch of the optical fibers is normally determined by their diameter. FIG. 9 is a sectional view of four optical fibers arranged parallel with one another. In this figure, a core 91 of each optical fiber 90 has a diameter of about 10 micrometers. A clad 92 is provided around the core 91. A coating 93 is provided around the outer periphery of the clad 92. An optical fiber array used to connect the plurality of optical fibers 90 together has an I/O terminal pitch equal to the pitch between the plurality of optical fibers bundled as shown in the figure. The coating 93 of the optical fiber has a diameter of about 250 micrometers, so that the I/O terminal pitch of the optical fiber array is about 250 micrometers. To change the I/O terminal pitch of the optical fiber array, the thickness of the coating 93 must be increased with the diameter of the optical fiber itself increased. Accordingly, it is very difficult to make an optical fiber array if the array comprises optical fiber I/O terminals each composed of multiple stages so that the vertical pitch of the array is different from its horizontal pitch or that the array has various pitches including larger and smaller ones.